Gene Mutation Flashcards
What is mutation and how does it relate to evolution?
Mutation is a change in the genetic sequence maybe altering the phenotype. This is how genetic change occurs. Natural selection preserves the best combinations for its environment. This is evolution.
Somatic Mutation
Occurs only in descendants of that cell (mitosis) - clone
Germline Mutation
Transmitted through gametes (meiosis - 1/2 of descendants are mutated)
When talking about results in gene mutation what generation are we referring to?
Second
Base substitution
Transition: pur-pur or pyr-pyr
Transversiton: pur-pyr
Insertions/Deletions/Frameshift Mutations
Caused by strand slippage or unequal crossing
Tautomeric Shift
Results in a transition mutation
T and G -> O=CH-NH3 -> OH-CH=N
C and A -> NH2-CH=N -> N=CH-NH3
Expanding Nucleotide Repeats
Increase in number of copies of sets of nucleotides - repeat copy number is in flux with each round of replication (can expand or contract)
Expanding Nucleotide Repeats - Inside coding sequence
Huntington’s
Expanding Nucleotide Repeats - Outside coding region
Fragile X
Forward mutation
wild type -> mutant
Reverse
mutant -> wt
missense
AA->diff AA (base substitution)
Nonsense
Stop (base sub)
silent
changes to same AA
neutral
AA change with no observable change (gly-ala)
loss of function
CF
gain of function
ex. larva growing legs where antenna are
conditional
temp sensitive
lethal
death
suppressor
2nd site mutation that hides effect of 1st mutation (rescue)
suppressor - intragenic (within gene)
may restore original AA
suppressor - intergenic
2nd mutation is a gain of function that binds to stop codon
DNA damage is caused by internal factors generated by what normal metabolic processes inside the cell?
- H2O (hydrolysis - H2O2)
- O2 (oxidation)
- alkylating agents
Spontaneous Mutation
occur under normal circumstances as a result of internal factors
Spontaneous Mutation - deletions/insertions
Spontaneous Mutation - depurination - break of what bond between 1’C of deoxyribose sugar? This creates what kind of site? What base is filled in?
break of covalent bond between 1’C of deoxyribose sugar creating apurinic site (A is filled in)
Spontaneous Mutation - deamination- loss of what base? What does it give rise to? What kind of transition?
loss of C group giving rise to U which pairs with A->T. This leads to a C->T transition
Spontaneous Mutation - mispairing (Wobble)
shift in backbone (2 H bonds) - like tautomeric shift but doesn’t use rare forms. G and T -> O=CH-NH3, C and A -> NH2-CH=NH
Induced mutations
Result of an exposure to external factors (environment chemicals/radiation). Increases mutation rate above spontaneous rate (mutagen)
Induced mutations - Base analogs
5Bru base analogue of T (pairs with A and G)
or
2-aminopurine base analogue of A and can mispair with C
Induced mutations - alkylating agents- what group does it add? Example? What kind of trnasition?
adds methyl/ethyl group (mustard gas) G->A transition
Induced mutations - deaminating agents - What acid? What transition? What base pair?
nitrous acid
C->T transition
U::A base pair
Induced mutations - hydroxylamine - What group is added to C? What does this increase? What transition is this?
adds hydroxyl group to C which increases occurrence of rare tautomers that pair with A
C->T transition
Induced mutations - Oxidative Radicals
hydrogen peroxide (transversions)
Induced mutations - intercalating agents - What is the result of sandwhiching induced mutation between adjacent base pairs? What mutation is this from? Example?
sandwich between adjacent base pairs distorting helix (insertions/deletions/frameshift) ex. ethidium bromide
Induced mutations - radiation - x rays (ionization)
breaks phosphodiester bonds = double stranded breakage
Induced mutations - radiation - UV
induces chemical bonds between two adjacent pyrimidines (thymidine dimers)
